• Structural Engineering and Mechanics
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• 제76권1호
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• pp.27-56
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• 2020

In this paper, the deflection and buckling analyses of porous nano-composite piezoelectric plate reinforced by carbon nanotube (CNT) are studied. The equations of equilibrium using energy method are derived from principle of minimum total potential energy. In the research, the non-local strain gradient theory is employed to consider size dependent effect for porous nanocomposite piezoelectric plate. The effects of material length scale parameter, Eringen's nonlocal parameter, porosity coefficient and aspect ratio on the deflection and critical buckling load are investigated. The results indicate that the effect of porosity coefficient on the increase of the deflection and critical buckling load is greatly higher than the other parameters effect, and size effect including nonlocal parameter and the material length scale parameter have a lower effect on the deflection increase with respect to the porosity coefficient, respectively and vice versa for critical buckling load. Porous nanocomposites are used in various engineering fields such as aerospace, medical industries and water refinery.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.527-531
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• 2007

The classical continuum theory-based thin film model is independent of their size and the surface effect can be ignored. But the surface to bulk ratio becomes very large in nano-size structures such as nano film, nano wire and nano beam. In this case, surface effect plays an important role and its contribution of the surface effect must be considered. Molecular dynamics simulation has been a conventional way to analyze these ultra-thin structures but structures in the range between submicro and micro are difficult to analyze by classical molecular dynamics due to the restriction of computing resources and time. Therefore, in present study, the continuum-based method is considered to predict the overall physical and mechanical properties of the structures in nano-scale, especially, for the thin-film. The proposed continuum based-thin plate finite element is efficient and reliable for the prediction of nano-scale film behavior.

• 인지과학
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• 제34권1호
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• pp.39-66
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• 2023

뉴미디어는 사회적 교류의 장을 인터넷으로 옮겨와 대규모 집단이 시공간의 한계를 뛰어넘어 한 곳에서 소통할 수 있게 만들었다. 최근 연구는 인간의 사회적 능력이 소셜 미디어를 통해 경험하는 확장된 집단 스케일을 따라가지 못하는 사례를 보고하기도 한다. 이러한 맥락에서, 본 연구는 인간의 사회적 정보 지각이 인구 집단 스케일의 확장에 영향을 받는지 다수편향 맥락에서 확인하였다. 인터넷 기반 과제를 통해 구성원의 수로 나타낸 집단 크기와 전체에서 특정 집단이 차지하는 집단 비율이 개인에게 지각되고 다수편향적 사회적 정보 활용에 영향을 주는 심리적 과정을 조사하였으며, 전체 집단 스케일의 확장에 각 과정이 영향을 받는지 살펴보았다. 집단 비율은 다수편향에 정적 영향을 주고 있으며, 그 관계는 비율 지각에 의해 부분매개 되었다. 전체 집단 스케일은 집단 비율과 비율 지각의 관계를 조절하지 않았다. 반면, 집단 크기와 다수편향의 상관은 유의하지 않았다. 전체 집단 스케일은 집단 크기 지각을 조절하였다. 전체 집단 스케일이 작은 조건에서 집단 크기와 크기 지각은 양적 상관을 나타냈지만, 전체 집단의 스케일이 확장된 조건에서 지각된 집단 크기는 유의미하게 작아졌고, 두 변수는 상관을 잃었다. 이러한 결과를 통해 집단 크기 지각과 관련된 심리 기제가 전체 집단 스케일의 확장에 제대로 반응하지 못하고 있음을 확인하였다. 나아가 집단 크기 정보를 처리하는 전문화된 심리 기제가 존재할 가능성과 다수편향이 특이적으로 받아들이는 자극의 형태를 진화심리적 관점에서 논하였다.

• 수산해양기술연구
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• 제47권1호
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• pp.1-9
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• 2011

In order to investigate the cause and magnitude of scale effect occurring in the model experiments of fishing nets, five pairs of Nylon pyramid nets and one pair of PE ones in which all the two nets paired were equal each other in the factors determining their flow resistance, i. e., the ratio d/l of diameter d to length l of bars, the angle f between two adjacent bars, the attack angle q of nettings to the water flow, and the wall area S of nets, and different in the values of d and l were prepared. Then, the nets were attached to the circular steel frame alternately and their flow resistances with shapes in water were measured on the sea ascribing no turbulent flows by using the tension meter made of a block bearing for the experiment. All the Nylon nets were spreads out easily in water to form a circular cone at relatively low velocity of water and showed the resistance smaller a little in the nets with larger d and l than them with smaller d and l, because the filtration of water through meshes become easier in nets especially with larger l. But PE nettings were not spread out sufficiently on account of their small flexibility and showed higher resistance especially in them with thicker twines. Therefore, the difference in bar length or mesh size and flexibility of nettings between prototype and model nets are regarded to become factors ascribing scale effect. Especially the influence of the difference in mesh size may become large significantly in actual model experiments because the mesh size of model nets is decided at much larger value than that given by scale ratio and so the difference of mesh size between the two nets become much larger than that between nets used in this experiment.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.413-417
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• 2004

Recent experiments have shown the 'size effects' in micro/nano scale. But the classical plasticity theories can not predict these size dependent deformation behaviors because their constitutive models have no characteristic material length scale. The Mechanism - based Strain Gradient(MSG) plasticity is proposed to analyze the non-uniform deformation behavior in micro/nano scale. The MSG plasticity is a multi-scale analysis connecting macro-scale deformation of the Statistically Stored Dislocation(SSD) and Geometrically Necessary Dislocation(GND) to the meso-scale deformation using the strain gradient. In this research we present a study of nano-indentation by the MSG plasticity. Using W. D. Nix and H. Gao s model, the analytic solution(including depth dependence of hardness) is obtained for the nano indentation , and furthermore it validated by the experiments.

• 한국연소학회지
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• 제5권2호
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• pp.63-68
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• 2000

Combustion phenomenon in scale-downed combustor is investigated. As the combustor scale decreases surface to volume ratio increases and chamber size approaches quenching distance. As the combustor scales down surface to volume ratio increases resulting increased heat loss. And this heat loss can affect quenching and instability of the flame. To investigate this effect plastic mini combustor is made. Stoichiometricaly premixed Hydrogen / air gas is used as fuel. Initial chamber pressure and chamber size are varied and the effects are evaluated. Peak pressure decreased with the decrease in chamber height. As initial chamber pressure decreases peak pressure decreases and this change is more important than scale down effect till the chamber height of 1mm. With this result and further information following the experiments design parameter for micro engine can be established.

• Structural Engineering and Mechanics
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• 제71권1호
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• pp.37-43
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• 2019

This paper studies application of modified couple stress theory and first order shear deformation theory to magneto-electro-mechanical vibration analysis of three-layered size-dependent curved beam. The curved beam is resting on Pasternak's foundation and is subjected to mechanical, magnetic and electrical loads. Size dependency is accounted by employing a small scale parameter based on modified couple stress theory. The magneto-electro-mechanical preloads are accounted in governing equations to obtain natural frequencies in terms of initial magneto-electro-mechanical loads. The analytical approach is applied to investigate the effect of some important parameters such as opening angle, initial electric and magnetic potentials, small scale parameter, and some geometric dimensionless parameters and direct and shear parameters of elastic foundation on the magneto-electro-elastic vibration responses.

• 대한통합의학회지
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• 제7권3호
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• pp.71-83
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• 2019

Purpose: This meta-analysis aimed to analyze to the effects of aquatic exercise programs in children with cerebral palsy and identify directions for future research. Methods: A systematic search based on the PRISMA guidelines was undertaken for studies conducted between 2006 and 2018 on aquatic exercise programs in children with cerebral palsy. A total of 10 studies were selected according to the inclusion criteria. The methodological quality was assessed using the Risk of Bias Tool for Randomized Controlled Trials (RoB) and Risk-of-Bias Assessment Tool for Non-randomized Studies (RoBANS). A meta-analysis software (CMA 3.0) was used to calculate the mean effect size, effect size by intervention (Halliwick and Watsu Aquatic methods), and effect size by outcome. Results: The mean effect size was 0.457. The effect size by intervention was largest for the Halliwick method, followed by the Watsu method. The effect size by outcome was largest for range of motion, followed by the gross motor function measure, the Pediatric Berg Balance Scale, and the Modified Ashworth Scale. Meta-regression analysis showed effect size increased when sample size, number of sessions, and length of sessions increased. Conclusion: The results show that aquatic exercise programs have a positive effect on children with cerebral palsy. Therefore, it is necessary to develop a guideline that recommends the appropriate intervention and the identifies the direction of future studies on aquatic exercise programs.

• 소성∙가공
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• 제22권7호
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• pp.394-400
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• 2013

Microforming is a very efficient and economical technology to fabricate very small metallic parts in various applications. In order to extend the use of this forming technology for the production of microparts, the size effect, which occurs with the reduction of part size and affects the forming process significantly, must be thoroughly investigated. In this study, the tribological size effect in microforming was studied using modeling and scaled ring compression experiments. A micro-scale friction approach based on the slip-line field theory and lubricant pocket model was used to understand the friction mechanism and explain the tribological size effect. Ring compression tests were performed to analyze the interfacial friction condition from the deformation characteristics of the ring specimens. In addition, finite element analysis results were utilized to quantitatively determine the size-dependent frictional behavior of materials in various process conditions. By comparing theoretical results and experimental measurements for different size factors, the accuracy and reliability of the model were verified.

• 소성∙가공
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• 제18권6호
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• pp.482-487
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• 2009

A finite element based microstructural modeling for the size dependent strengthening of particle reinforced aluminum composites is presented. The model accounts explicitly for the enhanced strength in a discretely defined "punched zone" around the particle in an aluminum matrix composite as a result of geometrically necessary dislocations developed through a CTE mismatch. The density of geometrically necessary dislocations is calculated considering volume fraction of the particle. Results show that predicted flow stresses with different particle size are in good agreement with experiments. It is also shown that 0.2% offset yield stresses increases with smaller particles and larger volume fractions and this length-scale effect on the enhanced strength can be observed by explicitly including GND region around the particle. The strengths predicted with the inclusion of volume fraction in the density equation are slightly lower than those without.